WPF入门教程系列五——Window 介绍

7.上面Buttom的Command类就是纯命令，什么参数都不接收，这次的ProvinceChangedCommand类在执行命令的时候，能够传参数！采用泛型的形式，给Action添加泛型参数。

8. 在Visual Studio 2022的解决方案资源管理器中，使用鼠标右键单击“Command”文件夹，在弹出菜单中选择“添加--> 类”，在弹出的“添加新项”对话框中，选择添加 “ProvinceChangedCommand”类，这是一个我们要实现的保存操作指令，然后选择“添加”。ProvinceChangedCommand的具体代码如下：

(资料图片)

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Input; namespace WpfGridDemo.NET7.Command{    public class ProvinceChangedCommand : ICommand    {        /// 
        /// 命令能否执行        /// 
        readonly Func _canExecute;        /// 
        /// 命令执行的方法        /// 
        readonly Action _execute;         /// 
        /// 命令的构造函数        /// 
        /// 命令需执行的方法        /// 命令是否可以执行的方法        public ProvinceChangedCommand(Action action, Func canExecute)        {            _execute = action;            _canExecute = canExecute;        }         /// 
        /// 判断命令是否可以执行        /// 
        ///         ///         public bool CanExecute(Object parameter)        {            if (_canExecute == null)                return true;            return _canExecute();        }         /// 
        /// 执行命令        /// 
        ///         public void Execute(Object parameter)        {            _execute((T)parameter);        }         /// 
        /// 事件追加、移除        /// 
        public event EventHandler CanExecuteChanged        {            add            {                if (_canExecute != null)                    CommandManager.RequerySuggested += value;            }            remove            {                if (_canExecute != null)                    CommandManager.RequerySuggested -= value;            }        }     }}void ProviceSelectionChangedExecute(object sender)        {            try            {                if (sender is ComboBox)                {                    ComboBox drp=sender as ComboBox;                    ProvinceCode=drp.SelectedValue.ToString();                    GridDbContext db = new GridDbContext();                    var list = db.City.AsTracking().ToList();                    List citys = list.Where(x => x.ProvinceCode == ProvinceCode).ToList();                    cityList = new ObservableCollection();                    if (citys != null)                    {                        citys.ForEach((t) =>                         { cityList.Add(t); }                        );                    }                     var cityCodes = from city in citys                                    select city.Code;                    List areas = db.Area.AsTracking().ToList().Where(x => cityCodes.Contains(x.CityCode)).ToList();                    areaList = new ObservableCollection();                    if (areas!=null)                    {                        areas.ForEach((t) =>                        { areaList.Add(t); }                        );                    }                }            }            catch (Exception ex)            {                throw ex;            }        }

结果如图：我们看到了省份下拉框中已经了省份信息。

9.通过绑定依赖属性，实现自动刷新需要实现以下三步：

1.Model继承并实现 INotifyPropertyChanged 接口；

2.数据集合使用ObservableCollection集合；

3.View使用Binding数据对象属性;

如果不行再看看集合在赋值前需要实例化，不然就出不来(必须要同一个源才行)

10. 在Visual Studio 2022中打开MainWindows.xmal文件，并将文件中的代码修改成如下：

                                                                                                                                                                                                                                                                                                                                                刷新保存            

using Microsoft.EntityFrameworkCore;using System;using System.Collections.Generic;using System.Collections.ObjectModel;using System.ComponentModel;using System.DirectoryServices.ActiveDirectory;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Controls;using System.Windows.Input;using WpfGridDemo.NET7.Entitys; namespace WpfGridDemo.NET7.ViewModel{    public class MainWindowVM: ViewModelBase    {        public MainWindowVM() {            cityList = new ObservableCollection();            areaList = new ObservableCollection();        }        private Area m_Area;        /// 
        /// 县镇区数据        /// 
        public Area AreaVM        {            get { return m_Area; }            set { m_Area = value; }        }        private string m_Province_Code;        /// 
        /// 省--代码        /// 
        public string ProvinceCode { get => m_Province_Code; set => m_Province_Code = value; }        private ObservableCollection areaList;          public ObservableCollection GridAreaList         {             get { return areaList; }             set             {                areaList = value;                 RaisePropertyChanged("GridAreaList");             }        }        private ObservableCollection cityList;         public ObservableCollection GridCityList        {            get { return cityList; }            set            {                cityList = value;                RaisePropertyChanged("GridCityList");            }        }            /// 
        /// 命令要执行的方法        /// 
        void SaveExecute()        {            try             {                GridDbContext db = new GridDbContext();                var list=db.Area.AsTracking().ToList();                Area modifyArea = list.Where(x=>x.Id==AreaVM.Id).FirstOrDefault();                if (modifyArea != null)                {                    modifyArea.Name = AreaVM.Name;                    modifyArea.Updated = DateTime.Now;                    db.SaveChanges();                }             }            catch (Exception ex)            {                 throw ex;            }        }         /// 
        /// 命令是否可以执行        /// 
        ///         bool CanSaveExecute()        {            return false;        }         /// 
        /// 创建新命令        /// 
        public ICommand ClickSaveAction        {            get            {                return new Command.SaveCommand(SaveExecute, CanSaveExecute);            }        }        //combobox        /// 
        /// 命令要执行的方法        /// 
        void ProviceSelectionChangedExecute(object sender)        {            try             {                if (sender is ComboBox)                {                    ComboBox drp=sender as ComboBox;                    ProvinceCode=drp.SelectedValue.ToString();                    GridDbContext db = new GridDbContext();                    var list = db.City.AsTracking().ToList();                    List citys = list.Where(x => x.ProvinceCode == ProvinceCode).ToList();                    var cityCodes = from city in citys                                    select city.Code;                    List areas = db.Area.AsTracking().ToList().Where(x => cityCodes.Contains(x.CityCode)).ToList();                    areaList.Clear();                    if (areas!=null)                    {                        areas.ForEach((t) =>                         { areaList.Add(t); }                        );                    }                     cityList.Clear();                    if (citys != null)                    {                        citys.ForEach((t) =>                         { cityList.Add(t); }                        );                    }                }            }            catch (Exception ex)            {                 throw ex;            }        }         /// 
        /// 命令是否可以执行        /// 
        ///         bool CanSelectionChangedExecute()        {            return true;        }        /// 
        /// 创建新命令        /// 
        public ICommand ProviceChangedAction        {            get            {                return new Command.ProvinceChangedCommand